1. Field of the Invention
The present invention relates to an apparatus for grinding a lens blank and more particularly to a lens grinding apparatus of the type including. means for storing the configuration of a lens frame.
2. Description of the Prior Art
A conventional method of manufacturing lenses is generally carried out by way of the step of first preparing an original pattern or master pattern on the basis of a certain lens frame on the pattern making machine and then mounting it on the contour carrying machine to grind a lens blank to the predetermined configuration corresponding to that of the V-shaped groove of a lens frame. However, it has been pointed out as drawbacks of the conventional method that it requires a large cast for installing manufacturing facilities particularly because of the necessity for the pattern making machine to prepare an original pattern from the lens frame. It takes a large amount of manpower and a long time because of the necessity for preparing the original pattern on the pattern making machine, manufacturing of lenses is achieved only at a very low operational efficiency and a lens blank cannot be ground precisely due to the frequent occurrence of dimensional error during preparation of the original pattern on the pattern making machine. To obviate the drawbacks as described above there has been previously proposed lens working apparatuses for grinding lens blanks while using a lens frame as a contour copying means. For instance, the applicant of the present invention invented an improvement of so-called direct copying type lens working apparatus as disclosed in Japanese Publication Patent No. 46817/1980 and 46818/1980 in which grinding of lens blanks is carried out while using a lens frame. It has been found that this improved apparatus brings high economy and excellent working accuracy and efficiency for a grinding operation.
However, the above-mentioned direct copying type lens working apparatus still has the following problems to be solved. Namely, when a metal frame widely used for eye glasses in recent years is employed for a lens frame, a follower roller on the copying arm is often disengaged from the frame due to abutment against the stepped portion on the junction area of the fgrame during the grinding operation of lens blank with the use of lens frame as contour copying means. As a result, the grinding operation is carried out at a reduced operational efficiency and therefore the lens blanks cannot be often reused. Thus, they are thrown away as refected goods. Further, a ground lens cannot always be tightly fitted to a lens frame when the grinding wheel wears irregularly or excessively. In this case, so-called repeated grinding operation is required which includes the steps of adjusting the center distance between the lens shafts and the wheel shaft on the lens working apparatus and then grinding the lens blank again. When a repeated grinding operation is carried out on the direct copying type lens working apparatus, it is necessary that the lens frame which has been removed from the lens working apparatus is reset to the latter and the lens blank is then mounted thereon. However, the resetting operation of the lens frame at the same position in the same direction after removal from the apparatus in that way requires highly trained skill and much time, but fails to assure excellently high fitting accuracy. Therefore, when repeated grinding operations are carried out on the direct copying type lens working apparatus, sufficiently high grinding accuracy cannot be expected.